• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.10 no.1
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• pp.7-14
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• 2014

There has been extensive experience associated with the operation of SGs wherein it was believed, based on NDE, that throughwall tube indications were present within the tubesheet. The installation of the SG tubes usually involves the development of a short interference fit, referred to as the tack expansion, at the bottom of the tubesheet. The tack expansion was usually effected by a hard rolling process and thereafter, in most instance, by the expansion of a urethane plug inserted into the tube end and compressed in the axial direction. The rolling process by its very nature is considered to be intensive with regard to metalworking at the inside surface of the tube and would be expected to lead to higher residual surface stresses. Alternate repair criteria(ARC) in the tack expansion area have been developed and applied to nuclear power plants in USA, however domestic nuclear power plants have not applied ARC for tubes in tubeheet area yet. In consideration of the degradation characteristics of tubes in the Steam Generator tubesheet, this paper suggests ARC application for tubes in the steam generator tubesheet of the domestic nuclear power plants in order to assure life time of the steam generator as well as nuclear power plants.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.9 no.1
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• pp.1-7
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• 2013

In around 2000, the U.S. NPPs have developed the various advanced engineering processes based on the INPO AP-913(Equipment Reliability Process Description) and showed the high performance in availability. With these benchmarking cases, the Korean NPPs have introduced the advanced engineering technology since 2005. The first step of the advanced engineering is to analyze and determine component importance for all components of a plant. This process is called Functional Importance Determination(FID). These results are basically utilized to determine the priority with limited resources in various areas. However, because the consistency of FID results is insufficient despite applying the same criteria in the existing operating NPPs, the degree of application is low. Therefore, this paper presents the improved methodology for FID interfacing system functions of Maintenance Rule Program and results of Single Point Vulnerability(SPV). This improved methodology is expected to contribute to enhance the reliability of FID data.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.12 no.1
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• pp.41-48
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• 2016

To investigate the effect of long-term thermal aging on the microstructural and mechanical characteristics of weldment made of nickel base alloy and its weld metal, an accelerated heat treatment was applied to simulate the process of long-term thermal aging in the operating condition of nuclear power plant. A representative nickel-based weldment with Alloy 600 and Alloy 182 was fabricated and heat-treated at $400^{\circ}C$ for 1,713 h and 3,427 h to simulate the thermal aging for the period equivalent to 15 and 30 years in operating pressurized water reactors, respectively. The microstructural and mechanical characteristics were analyzed by using optical microscopy, scanning electron microscopy and Vickers microhardness measurement. Changes were observed in precipitation behavior and microhardness of each specimen, and these changes were mainly attributed to the change in precipitated morphology and residual stress across the weld during the thermal aging process.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.1
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• pp.33-38
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• 2012

A PHE (Process Heat Exchanger) in a nuclear hydrogen system is a key component required to transfer heat energy of $950^{\circ}C$ generated in a VHTR (Very High Temperature Reactor) to a chemical reaction that yields a large quantity of hydrogen. Korea Atomic Energy Research Institute has established a small-scale gas loop for the performance test on VHTR components and recently has manufactured a medium-scale PHE prototype made of Hastelloy-X. A performance test on the PHE prototype is scheduled in the gas loop. In this study, high-temperature structural analysis modeling, and macroscopic thermal and structural analysis of the medium-scale PHE prototype by imposing the established displacement boundary constraints in the previous research were carried out under the gas loop test condition. The results obtained in this study will be compared with performance test results.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.1
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• pp.49-55
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• 2021

In this paper, an application example for fitness-for-service of material is shown. A kind of instrument valve is made of austenitic stainless steel fabricated by the cold working process. The tensile strength of the cold worked austenitic stainless steel has to be limited under 90 ksi to prevent the stress corrosion cracking in power plants. In industrial fields, tensile strengths of some materials were discovered to be over the regulation requirements in a certified material test report (CMTR). Owner's verification tests were performed to compare with that in a CMTR and to check the appropriateness. It is found that, in the case of verification test under the required test speed, valve materials could be used in the field. Although it is only one application sample of material check process in the power generation site, this case study could show an importance of basic experimental technology in academia and research circles.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.100-100
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• 2009

This paper is concerned with numerical analyses of residual stresses in welds and material's susceptibility to stress corrosion cracking (SCC) for the primary piping system in nuclear power plants: Both the dissimilar metal weld (DMW) for stainless steel to low alloy steel joints and the similar metal weld (SMW) for forged stainless steel to cast stainless steel joints are considered. Thermal elasto-plastic analyses using the finite element method (FEM) are performed to predict residual stresses generated in fabrication welding and its related processes for both the DMW and SMW, including effects of quenching for cast stainless steel piping, machining of the DMW root, and grinding of the SMW root. As a result, the effect of quenching should be included in the evaluation of residual stresses in the SMW for the cast stainless steel piping. It is deemed that residual stresses in both the DMW and SMW would not affect the SCC susceptibility of the welds providing that the welding processes are completed without any weld repair on the inside wall of the joint. However, the grinding process if performed on the safe-end to piping weld, would produce a high level of residual stresses in the inner surface region and thus a stress improvement process (e.g. buffing) should be considered to reduce susceptibilities to SCC.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.33-39
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• 2019

in 2010s, many factories are operating without any safety guarantees due to the aging process. Although it is difficult to fundamentally solve the problem of aging process and equipment, Prevent risk by risk assessment in advance. This study targets the corrosion caused by sulfur in the piping in the CDU(Crude Distillation Unit) process desulfurization equipment and conducts the risk assessment by RBI(Risk Based Inspection) referring to API RP 581. RBI expresses the risk by combining frequency and consequence, and creates a risk matrix based on these expression. In this study, the hole size of the pipe was selected as Small and Medium, and the sensitivity of the frequency was selected as 'Low'. You can refer to the Risk Matrix created from the standard to evaluate the risk of corrosion of sulfur from pipes in the piping and to plan future accident prevention. Similarly, prevention of aging in a similar way can prevent large and small incidents that are not visible.

• Journal of the Korean Applied Science and Technology
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• v.31 no.4
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• pp.669-678
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• 2014

The amount of waste water generated from the domestic sources is consistently increasing in proportion to economic growth, and the conventional activated sludge process is widely being used for general waste water treatment. But the ministry of environment becomes stringthent treatment standards of N and P (less than 20mg/L of N, 2mg/L of P) to prevent the eutrophication of lake water, and therefore highly advanced treatment technology is required not only in the existing treatment plants where the activated sludge process is being used, but also in newly constructed treatment plants for the treatment of N and P. This study is aimed at highly operating the engineering technology method was developed by domestic to eliminate N and P at the same time. Experiments were conducted in the treatment plant located in Yong In city. The bioreactor was started from the principal equipment for the elimination of N and P and the elimination of organic compounds. It consists of an internal recycle piping from the end of the aerobic tank to the anoxic tank and external recycle piping from the final settling basin to the denitrification tank. By experiment of 4 types separate inflow of waste water to the denitrification tank and the anaerobic tank, and changes in staying time at the anoxic tank and the aerobic tank, the elimination of organic compounds in each type and the relationship in the efficiency between the elimination of N and P were researched.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.18 no.2
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• pp.87-100
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• 2022

Unit capacity factor (utilization rate) of nuclear power plants (NPPs) is an important performance indicator. Since the first commercial operation of Kori Unit 1 began in April 1978, the utilization rate of domestic NPPs has gradually increased, reaching 90% from the end of the 1990s. However, due to various issues such as the Fukushima accident in 2011, corrosion of the CLP, the utilization rate dropped to 65~80%. In the early 1980s, the utilization rate of the U.S. NPPs was around 60%. However, since 2004, it has been consistently maintained above 90%. Therefore, in this study, we first examined the causes of declining the utilization rate in domestic NPPs. Next, the significances of the utilization rates are reviewed in five aspects: investment capability, electricity rate, safety and export, etc., with discussion on the current status of the utilization rates in the U.S. Based on this, three key factors are derived as the reasons of the increasing: equipment reliability program, on-line maintenance and the pursuit of institutional rationality. And finally, by synthesizing above results, the measures for increasing the utilization rate of domestic NPPs are proposed in terms of equipment management, institutional improvements, and personnel resources.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.12 no.2
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• pp.40-49
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• 2016

Flow accelerated corrosion (FAC) of the carbon steel piping has been a significant problem in nuclear power plants. FAC occurs under certain hydrodynamic, environmental, and material conditions, and extensive research into the factors of FAC has been conducted. The basic process of FAC is now relatively well understood; however, a full mechanistic model has not yet been established. Recently, the Korea Atomic Energy Research Institute (KAERI) has built a large experiment loop system for FAC. To produce significant experimental results using this system, the factors affecting on FAC should be analyzed quantitatively, and a model needs to be developed. In this work, a statistical modeling methodology to develop an empirical model is described in detail, and a preliminary model is suggested. Firstly, FAC data were collected from the research literature in Japan and the results of domestic experiments. The flow rate, water temperature, pH at room temperature, and the Cr content are selected as major factors, and nonlinear regression is used to find the best fit of the available data. An iterative procedure between suggesting and evaluating a model is used until an optimum model is obtained. The developed model gives the FAC rate comparable to the measured FAC rate. The developed model is going to be refined using additional laboratory data in the future.